Pallets for transporting and storing relatively heavy manufactured articles have traditionally been constructed of wood and metal and, in more recent years of plastic. Soft wood pallets are widely available and easily constructed, but because of the variability of timber characteristics the load carrying capacities and lifetime of wooden pallets are unpredictable. Furthermore, when, due to ordinary wear and usage a wooden pallet must be junked, there is very little salvage value in the scrap wood. Wood pallets are also subject to breakage, thus are not reusable over an extended period of time. Wood pallets also take up a considerable amount of valuable floor space in the factory or warehouse when they are not in use.
Steel pallets, while having increased strength characteristics, are expensive to manufacture. Both wood and steel pallets can be of considerable weight and neither are easily recycled, resulting in additional costs for disposal at the end of their useful life.
Plastic pallets have been gaining increased acceptance due to factors such as consistent physical characteristics and load-carrying capacity, high strength-to-weight ratio, resistance to corrosion, and durability. Plastic pallets also can be manufactured relatively economically to relatively close overall outside dimensional tolerances. Such pallets can also be made with relatively wide, flat planar supporting surfaces, rendering them particularly well adapted to be supported and easily moved on conveyors and the like having live or gravity rolls, "slide-by" side guide walls, automatic track switching arrangements and other automated equipment.
As a result of these and other factors, attempts have been made to develop lightweight plastic pallets that are relatively economical to manufacture but which are of sufficient strength so as to be capable of supporting and handling the large, heavy loads customarily associated with wood and metal pallets. In one generally successful form of plastic pallet design, upper and lower plastic sheets are vacuum formed in separate molding operations in juxtaposed but separated molds. The two sheets are then selectively fused or "knitted" together by closing the molds together to thereby form a reinforced double wall or "twin sheet" structure. Such twin sheet thermoformed plastic pallets may be made on vacuum forming machines such as those shown in the U.S. Pat. Nos. to Brown 3,583,036; 3,787,158; and 3,925,140.
These twin sheet plastic pallets, although substantially more durable and dimensionally accurate than the wooden pallets they replace, tend to have a substantially higher initial cost than the corresponding wooden pallets due in large part to the relatively high cost of the raw plastic material required to form the pallet. Typically the top and bottom twin sheets of the pallet are made by vacuum forming sheets of organic polymeric material, such as high density polyethylene. It is therefore critical that the twin sheet type of pallet embody a structural design that maximizes the structural strength of the pallet for a given amount of plastic material employed to form the pallet. Accordingly, twin sheet plastic pallets need to be designed to take maximum advantage of the materials used by maximizing the load capacity for the given amount of material used in forming the pallet. Thus the top and bottom pallet deck sheets are vacuum mold formed respectively having dependent and upstanding peripheral side walls joined to one another along a peripheral seam line by fusion of the thermoplastic material while at an elevated temperature and under the pressure of the forming press. This overall configuration thus forms a generally flat, pancake-like hollow clam shell structure having a high strength-to-weight ratio. Additionally, prior art efforts to increase the structural strength of the pallet have included providing a plurality of recessed channels, ribs, pockets, etc., which extend inwardly transversely from the outer major plane of the pallet top and bottom sheets respectively. The two sheets are also selectively fused or knitted together in the press where these interior surfaces of these respective indentations meet and abut in the interior closed space of the pallet. The structures formed by the downwardly depending and upwardly projecting bosses, ribs, etc., fused together provides a rigid reinforced structure which resist deformation of the deck (in addition to reinforcement provided by the fused-together peripheral side walls of the top and bottom sheets).
Another important parameter in the construction of such twin sheet plastic pallets is stackability when empty to minimize storage space and return-transport storage volume. Various complementary nesting configurations have been provided in the opposed planar surfaces of the stacked pallets to facilitate such stacking in a secure stable array.
Whereas such twin sheet pallets of the prior art have been highly successful and have been widely commercialized, hitherto so far as is known, such pallets have not been successfully constructed to have the capability of reliably transporting relatively bulky, heavy and expensive loads such as manufactured subassemblies, particularly those having a high load profile relative to pallet profile, such as automotive vehicle passenger seats. Accordingly, heretofore such vehicle seats have been packaged individually in cartons or boxes at the seat manufacturing facility, usually located geographically relatively remote from the automotive final assembly plants, shipped or transported as so containerized, and then handled as packaged goods at the assembly plant for sorting, unpacking and delivery to the assembly stations along the assembly line. These operations require care in preventing damage to the natural or synthetic textile, leather, vinyl sheet and/or seat coverings as well as to the frame and vehicle floor mounting structure of the seats. These as well as other factors have hitherto made the vehicle seating the next most expensive component of the vehicle, after the engine, to manufacture and install in the vehicle. While other vehicle components have been successfully palletized, as plural groups of identical components, hitherto palletization of automotive passenger seats, so far as known, has not been deemed feasible or successfully accomplished utilizing plastic pallet technology available to date to provide twin sheet type pallets adapted for automated roll-conveyor selection, sorting and delivery to assembly line stations to thereby significantly reduce vehicle assembly costs.
Another serious problem posed by shipping, storage and assembly of automotive passenger seats for many types of automotive vehicles resides in the potentially large number of different seat frame constructions encountered to satisfy the variety of seating options currently provided to the customer for a given vehicle. For example, in one popular mini-van vehicle of American manufacture, namely the "Windstar" mini-van model currently manufactured by Ford Motor Company of Dearborn, Mich., eight different interior seating arrangements and combinations are provided utilizing six different seat frames namely: (1) bolt-on-permanent mount type front driver-side single bucket seats, (2) bolt-on-permanent mount type front passenger side single bucket seats, (3) removable mount two-passenger second row bench seats; (4) removable mount three-passenger third row bench seats; (5) driver-side removable mount single-passenger second row bucket seats; and (6) passenger-side removable mount single-passenger second row bucket seats. The selection of the given assortment of these seat types to provide any one of the eight seating arrangements to satisfy customer orders or provide dealer inventory variety for this mini-van has thus posed an expensive supply and assembly problem for the vehicle manufacturer using hitherto available automotive seat carton or container-type packaging, shipping and storage procedures and equipment.